Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $154.68   6.786%   $165.1766   $165.18   $165.20   $165.20  
  Purchase #2 $104.79   10.402%   $115.6903   $115.69   $115.70   $115.70  
  Purchase #3 $77.34   7.575%   $83.1985   $83.20   $83.20   $83.20  
  Purchase #4 $38.97   3.312%   $40.2607   $40.26   $40.25   $40.30  
  Purchase #5 $132.45   12.867%   $149.4923   $149.49   $149.50   $149.50  
  Purchase #6 $236.88   5.699%   $250.3798   $250.38   $250.40   $250.40  
  Purchase #7 $140.60   4.269%   $146.6022   $146.60   $146.60   $146.60  
  7 purchase totals = $885.71       $950.8004   $950.80   $950.85   $950.90